Since a compressor provided in a cooling system of a vehicle air conditioning apparatus is directly connected to an engine through a belt, its RPM cannot be controlled.
Thus, in recent years, variable displacement compressors are widely used to vary an amount of discharged refrigerant to achieve a cooling capacity without being restricted by the RPM of an engine.
A variety of types of variable displacement compressors such as a swash plate compressor, a rotary compressor, and a scroll compressor are currently disclosed.
A swash plate compressor is configured such that a swash plate installed within a crank chamber rotates while its rotary shaft is rotating and a piston reciprocates during rotation of the swash plate, in which case an inclined angle of the swash plate is varied. Then, a refrigerant in a suction chamber is suctioned into a cylinder, compressed, and discharged into a discharge chamber during reciprocation of the piston such that an inclined angle of the swash plate can be varied according to a difference between a pressure in the crank chamber and a pressure in the suction chamber, making it possible to regulate an amount of discharged refrigerant.
In particular, an electronic solenoid type displacement control valve is employed to be opened and close to adjust a pressure in a crank chamber using flowing currents and thus adjust an inclined angle of a swash plate to regulate a displacement of discharged refrigerant.
Then, during an operation of a capacity control valve, signals for a detected RPM of an engine, interior and exterior temperatures of a vehicle, and a temperature of an evaporator are processed by a control unit equipped with a CPU, and currents are sent to an electronic coil of a displacement control valve based on the processing result.
A general example of a displacement control valve for a variable displacement compressor is disclosed in U.S. Pat. No. 6,443,708 (hereinafter, referred to as “conventional technology”). Hereinafter, a configuration of the conventional displacement control valve for a variable displacement compressor will be schematically described with reference to FIG. 1.
As shown, the conventional displacement control valve 20 for a variable displacement compressor includes a valve housing 40, a valve body 30, and an electronic solenoid such that the valve body 30 reciprocates to open and close a discharge chamber connecting hole 6 formed in a valve housing 40 as currents flow through the electronic solenoid.
A suction chamber connecting hole 8, a crank chamber connecting hole 5, and a discharge chamber connecting hole 6 are formed in the valve housing 40 to receive pressures in a suction chamber, a crank chamber, and a discharge chamber respectively. The discharge chamber connecting hole 6 and the crank chamber connecting hole 5 are communicated with each other.
The valve body 30 is configured to reciprocate as currents flow through the electronic solenoid to open and close the discharge chamber connecting hole 6 when it passes through the crank chamber connecting hole 5 while reciprocating. A spring 28 is installed at a lower portion of the valve body 30 to lower the valve body 30 in a normal state where there is no external force and thus open the discharge chamber connecting hole 6.
The electronic solenoid includes a movable rod 24 connected to the valve body 30, and an electronic coil 21 disposed at a circumference of the movable rod 24. A movable core 23 is installed at an end of the movable rod 24.
However, according to the conventional technology, since the valve body 30 is configured to be closed when it goes from the crank chamber connecting hole 5 to which a crank chamber pressure Pc is applied toward the crank chamber connecting hole 6 to which a discharge chamber pressure Pd is applied, the area of the discharge connecting hole 5 is too large in a valve where a pressure difference Pd−Ps is used as a parameter for an opening degree of the valve, causing the valve body 30 to be slim.
That is, since a pressure Pd is applied to a cross-sectional area of the valve body 30, if the area where the pressure Pd is applied is too large, a valve opening force applied to the valve body 30 becomes excessive, causing a current applied to the electronic solenoid to close the valve body 30 to increase and an amount of generated heat to become larger.
Accordingly, the productivity of the displacement control valve 20 is severely lowered.